[LEDE-DEV] lede integration issues remaining from the detrius of cerowrt

[Daniel Curran-Dickinson]

Hi David,

Thanks for the good info on wear levelling; apparently I was misinformed
on the topic.


On Thu, 2016-06-16 at 01:03 -0700, David Lang wrote: [snip] 
> >>> To a certain extent though, I question the need for something as restricted as OpenWrt
> >>> for the new bigger devices anyway; there are elements like netifd that would be good to
> >>> see continue, but I'm not sure that most of OpenWrt really makes as much sense when you're
> >>> not needing to squeeze maximum use out of very erase block, and that therefore, while it
> >>> may be a smaller market/mindshare, that focussing on the the true embedded type scenario,
> >>> seems to be more of what LEDE's niche is.
> >>
> >> LEDE/OpenWRT is a good fit for any device that operates on raw flash instead of
> >> a hard drive or ssd with wear leveling. Once you have storage that you don't
> >> worry about wearing out and is large enough to hold a normal Linux Distro, it
> >
> > makes sense to move to such a distro and update packages individually.
> >
> > Hmmm...the wear levelling thing is confusing.  I was told by someone who I thought knew
> > what they were talking about, that flash chips included some form of hardware-based
> > wear levelling built in already.  Apparently that is was inaccurate (hardware-level
> > support is something I only having minor knowledge of; it's not the part the interests me,
> > nor where I have worked on it for any length of time; I'm more interested in what you can
> > do with existing hardware support combined with software rather developing the core support
> > itself).
> 
> raw flash chips like we have in a router have nothing.
> 
> flash chips packaged in SD cards, USB drives, etc commonly have very primitive 
> wear leveling (in many cases only targeted at the places that the FAT filesystem 
> is going to use)
> 
> flash chips packaged into SSD drives or anything more sophisticated tend to have 
> very extensive wear leveling setups, and will move existing, unmodified data if 
> needed to balance things.
> 
> I haven't looked recently, but a couple years ago the idea of having an 
> in-kernel flash wear leveling capability was getting a lot of discussion on the 
> kernel mailing list. I din't remember seeing what finally happened with that.
> 
> For the very tiny devices, it doesn't make sense to try and make use of 
> something like that (it takes more space ond isn't going to apply to a static, 
> pre-build compressed filesystem)
> 
> But for the overlay filesystem where new stuff may get added on newer devices 
> that have the much larger NAND flash, it may be something to look into, even 
> though it complicates the base config for such systems.
> 

Okay, I understand a lot better where you are coming from now, since I
was under a misapprehension about the capabilities of the hardware.  In
this case I agree we need to do some work to support these bigger
devices including things like wear-levelling, and that this is
definitely a space in which LEDE can be relevant going forward.

Regards,

Daniel